Loud-speaker horn



Jan. 9, w KLlPscH 7 2,537,141

LOUD-SPEAKER HORN Filed June 15, 1945 28heets-Sheet 1 Fqw. W. A L/PSCH INVENTOR.

- BY fM ATTORNEY.

Jan. 9, 1951 w, psc 2,537,141

LOUD-SPEAKER HORN Filed June 15, 1945 2 Sheets-Sheet 2 P4111. 14/. 1% /FS// fi INVENTOR. L I ,l L l BY KM ATTORNEY.

Patented Jan. 9, 1951 U-N'l'lED STATES PATENT OFFICE LOUD-SPEAKER- HGRN Paul W. Klipsch, Hope, Ark.

Application J "one 15, 1945, Serial No". 599,642

6 Claims.

The invention. relates to horns for loudspeakers, particularly to; those intended for the middle and highs. audio frequencies and: for the: achievement oi specifieda wide angles of radiation.

One object; of. the invention is to. provide a horm for; the'hi'gh frequencies: to complement the low" frequency horn or' Woofer disclosed in UL. Si Patent N01. 2,3 10,243 issuedv February 9.3.1843, and Patent. Noz. 2,373,692 issued April. 137-, 1945-, the required. complementary performance. being that of transmitting the: frequency range from about 400 cycles per: second. and higher and radiairing. into; an. angle about 90 wide and a solid angle" 0t: 1/2: steradiansg Broadly, an object of the invention is to pro"- vide: a. horn of desired angular" radiation in the smallest: possible; length and space commensurate with. the requirements of mouth size, throat size and taper rate, at the same. time maintaining such: bends as are necessary tominimum angles and to-placethem at regions i'nthe conduit where the: radii of the bends? can be kept small and the bendi. curvature: smooth A specific object is to provide a horn in which expansion. takes place in at single: plane for a portion. off the: horn. length to bring the radiation angle up to the desired limits in: thisplane, then expansion takes place at right angles to said first plane while. continuing to expand in the wedge angle: reached in the firstv expansion" Ex pansion continues until the desired mouth area is accomplished.

Another object is to provide a. horn having? cooperating side-walls and baifies so constructed.

and arranged that the radiation angle of. the horn: is determinedbythe outer surface boundaries or wallsof. the horn nearest the mouth.

It is also an object to provide a horn of the class described including at least one set of cell bafileswhich terminate short of the mouth of the hornwhereby theindividual cell mouths are small compared. to the shorter wave lengths to be radiatedl.

The foregoing are primary objects which, together with other objects and advantages will be more fully apparent from the following description t'akenin connection with the accompanying drawings. in which Fig. 1 shows an oblique perspectiveview of one:

embodiment of. the invention;

Figs. 2'. and 3v show respectively topand side exterior views of the horn shown in Fig. 1;

Fig.4 isa horizontal sectional view of the horn takenon. line 4-4 in Fig. 5,. the driving; motor being shown attached thereto;

1. lei-21);

Figs 5 is a vertical sectional view of the horn taken; on; line. 5--5 in. Fig. 4;

Fig. 6 is an enlarged sectional view of. the portion proximate the throat and illustrates" how the taper progresses from circular: to rectangular section; in a short. length;

Fig. 7' shows one possible alternative" of baille arrangement at the mouth; and;

Fig; 8 shows two units with motors attached, so arranged. as: to give: 180 radiation angle.

It; shouldi be: understood. that the terms. top and side are used to simplify terminology and not: tov imply any limitation in the; positions in which. the hormor'horns may be used.

Generally; speaking, andlsubj act to several limitations; the radiation. angle of a horn: is" determined. by the angle: formed between the outer surface boundaries or: walls of the horn nearest the mouth.v Roughly, extrapolation of. the walls of the horn. outwardi into space. will: define the radiation angle. However; this general'. idea holds only if suitable deflectors within the horn force the sound to follow the curves of the outer: horn boundaries and is further subject to limitations relative to mouthisize.v In the prior art-the multicellular; horn consists ofa cluster-of small horns, all identical and: grouped to direct the sound throughout a given solid; angle; such a; horn is shownand discussed by Wente' and Thuras Auditory lkerspectivLe -Loudspeakersv and Micro phones? Electrical liingin'eering, January 1934, pages 1724. An example of an asymmetrical multicell is that: taughtby the: Wente Patent No. 2 ;,61'0 which expansion takes place: simultaneously' atldifferent. ratesintwoplanes, and the directive properties: in one plane as well as ex pansionrat'e are controlled by inserted deflectors;

The limitations: oiv directivity arise from the relation of mouth size to the transmitted wavelength; and? manyother factors. H. F. Olson, his book; Elements of Acoustical- Engineering-F McGrawHiil, 1940; discusses"- directional charac-- teristics andi gives' an. excellent? bibliography of the wholesubjecti. From. this and: other sources,

it becomes evident that ideal directional characteristics can. only be approached From the published; discussions on multicell horns the limi tations' of total! mouth size, individual cell size; angle between cells and: the taper rate Will be realized-1 In the various attempted designs to achieve specifically a: high frequency speaker to supplement the aforementioned woofer-s the applicant soona found that the conventional m'ult'i cell: does not lend itself: tothe shapes necessary for the desired angular characteristics Thepres 3 ent invention comprises a pronounced improvement thereover and more closely approaches the desired ideal.

The present invention contemplates a multicellular arrangement in which at least one set of cell bafiies terminates considerably short of the mouth, whereby the individual cell mouths are small compared to the shorter wave lengths to be radiated so that a small number of such baflles can sufiice and still function as true deflectors. In the conventional symmetrical multicell, the separate cells tend to act as separate horns at the higher frequencies with resultant formation of sharp beams. By continued subdivision this could be avoided but is deemed impractical by Wente and Thuras in their paper already referred to on Auditory Perspective; their remarks on The High Frequency Horn, pages 21-22, apply. This impracticality can be avoided by the present invention. It should be pointed out that, once the wave front has been formed to the desired radius of curvature, the wave acts as its own guide, needing no further deflectors.

: The aforementioned low frequency speaker, designed to operate in a room corner, radiates into substantially 1r/2 solid angle. Ideally, the

supplementary high frequency speaker should radiate into the same angle for several reasons,

two or which are: first, to get adequate coverage centration of sound by one speaker into a smaller I angle than that into which the other speaker radiates,

. .Ideally both speakers will have the same directivity characteristics throughout the frequency range of each. Generally speaking this is impossible except in prohibitively large structures. But, if the directivity and frequency response characteristics approach reasonably close to. the ideal, there, should be no necessity to equalize either channelnor the system as a whole except perhaps at the extreme low and high ends of the spectrum. V

The present invention as shown in the embodiment of Figs. 1 to 6 comprises the horn structure I having two regions of expansion generally indicated at 2 and 3, of which the former extends from point B to point D while the latter extends outwardly from point D. The region 2 comprises a pair of parallel top, and bottom walls 4 and 5 and side walls 6 and I perpendicular thereto and extending divergingly outwardly so that expansion in this region takes place in a single plane and brings the radiation angle up to the desired limits in this plane. In the region 3, beyond D, the divergence of the side walls 6 and 1 is constant but the walls 4 and 5 merge into converging top and bottom walls 8 and 9 which determine the radiation angle in a vertical direction.

, It seems apparent from reference to Fig. 4 that the. expansion in the region 2 extending from C to D takes place all in one plane, without expansion at right angles to such plane. Attention is also directed to the fact that the terminal portion of this region includes the cell baflies to which reference is above made.

These comprise a central baffle 12 of which the rearward portion I2 provides an initial bifurcation and gentle lines of curvature forwardly from the throat. Proxlmate the forward end of the bafiie portion i2 each air column is again bifurcated by means of contour surfaces I0 on the sidewalls t and 5 and similar surfaces H on the central baffle I2 cooperating with deflectors [3. This construction provides desired deflectors for the sound waves and also desirably controls the flare rate.

From the region D to the mouth It, expansion continues at the angle established in region CD in the plane shown, and expansion commences in the plane at right angles thereto. Fig. 5, the view taken at right angles to that of Fig. 4, shows one way of treating the mouth section to obtain a desired angle, namely 60 in a given length, and shows also the non-expansion in the CD regions in this plane. It is to be noted that the structure as shown in this figure includes a single horizontal bafile ll whereas the structure shown in the alternate structure of Fig. 7 comprises curved bafiles I8 cooperating with surfaces 8' and 9 which are curved complementarily.

The expansion from the throat section at A, to section B, may take place in any convenient manner, for example, for a driving motor 15 with circular throat, the expansion should be from the circular throat to a square cross sec tion by providing an inner filler member l6 secured to the inner walls and having the configuration as shown in Fig. 6, and then to whatever size rectangular section may be chosen at section C.

In the particular design shown, the cross section at C is one inch square which results in a very small difference between minimum and maximum path lengths through the first bend or rather, gentle curve. This design provides a minimum of interference at the point where the divided cellular air columns rejoin. Theoretically the horn shown should operate effectively throughout the upper portion of the audible register. Listening tests and microphone measurements indicated uniform field within the contemplated angles.

It is not to be expected that the horn of the present invention would improve upon the angular radiation characteristics of an ideal multicell horn of equivalent mouth and outer wall conformation; rather, the present invention aims (l) to make possible a nearer approach to ideal mouth and wall conformation for wide angle radiation with limited horn lengths and (2) to hold the phase of radiation over different parts of the mouth area such that the wave front is a spherical surface with the location of its center as invariant as possible with respect to frequency. That is to say, the present invention recognizes the impossibility in a symmetrical multicell of attaining uniform wave phase at the surface Where the cell joins the non-cellular parts of the horn except when the total angle of radiation is limited, and hence the waves do not emit from design a conventional multiceil of bhe same length 7 and cut-off as the horn illustrated herewith re- 5 sulted in either poor phasing of the wave fronts;v the individual cells, or else a smaller amgle of radiation than desired.

The: terms multicell, conventional: multicelLf multicel-lular horn, etc are; used herein o: mean the, type or"- horn depicted in Fig. 2.11 of. the hereh' before referredto "Elements; of. Acous tical, Engineering, by Olson. The term asymmetrical multicell" is u ed to designate the type of: horn described herew h, or such a born as. described the aforementi .aed Wente Patent. Nor. 2-.1i3 5r,. lt.- wherein the cellv mouths are. no square, and the cell, axes are not. necessarily traight.

This speaker was specifically designed to operate with the aforementioned Woofer? The: woofer dimensions, (see Journal; of: the Acoustical Society of America, vol. No. 2, pp; 137-144., October 1941, also. vol. l i. No. 3,131 179482, January 1943. as well as Patent No. 2373.692) are. anproximatel length, diagonal from corner, 2:3; with across wings, 39"; heighth 39".. The frequency response is roughly from 40, to 400, cycles. The cross-over network crosses at 400 cycles. In order to cover the same radiation solid angle as the woofer, and also to obtain the desired angular coverage, the horizontal and vertical angles for the H. horn were selected asrespectively 90 and 60. The space limited the cut-off frequency to 33% cycles when using a Western. Electric 555 W driving motor with approximately 0140. square inch throat area. With this; thioat size,v available le th, and given fiare-cut-ofi'. the mouth. size available is about 254,0; square inch more than adequate to prevent; severe reflections. at too cycles, and sufficient to give the desired, directionalv properties. The drawin s are. rou hly to. scale,.the. length of. horn from throat fitting. to. mouth being approximately 21 inches. Flor the. pilot model most of the Walls are of plywood. The deflectors are of soft pine. The mouth arrangement of Fig. 5 Was chosen as the easiest to construct as well as giving the desired vertical. spread. application of a coat of varnish serves to harden the soft wood surfaces and prevent surface absorption of the higher frequencies.

In the experimental model the sectional wall thickness was built up by gluing 2 sheets of inch plywood together and then rasping to the desired contour to give th desired vertical expansion through the DE region, and from E to the mouth, inch ply material known in the building trade as Tekwood was used to generate the two conical surfaces which are best delineated in Fig. 1. As a manufactured product the entire top and bottom surfaces would better be molded, say, from a post-forming plastic sheet, or perhaps from wood plies laid in a suitable mold and bonded in the desired contour by the fluid pressure method and high-frequency heatmg.

The foregoing details are intended to disclose the invention in a manner to enable the skilled artisan to construct a horn embodying the invention, but are not to be implied as limitations on the claims. Obviously, almost any angular limits can be met, and the wider the angle, the greater will be the advantage of the present invention over the existing art. Any feasible construction method may be employed, and any rigid materials may be used, such as wood, metal or plastic.

I prefer to place the horn cut-01f as far as possible below the crossover frequency, and to place about: 18; decibels to 30 decibels, per octave: loss, in the attenuation region of the high pass filter to, keep the electrical power fed to; the speaker below its cut-off frequency as lowas possible, as suggested in- Woofer-Tweeter Cross.- over Network, Electronic -Nov. 1945,, pp. 144,- 145. This prevents driving the diaphragm through large excursions the frequency range where little. or no acoustic loading exists. It large diaphragm excursioa cycle horn should occur, say, 209 cycles, harmonics of. this frequency would be generated and: the. harmonies would propagate through the horn resulting in: rough performance. The lowpass. part of the crossover network needs only, say, 6. deci-bles per octave attenuation above crossover; In a horn of the length, cut-oil frequency, and mouth size described, the cutoff ofv 3-30 cycles. permits adequate loading to at. .nd about the crossover frequency moo cycles) so thatvery little distortion occurs. The questions of. harmonic generation by allowing appreciable power below the horn, cut-off frequency to reach thevoice coil are discussed in copend'ing: application 586,786 filed April 5, 1945,. now abandoned, and

also in apaper Note on Acoustic: Horns,

by Paul W. Kli-psch, Proc. 1'. R. July 19.45;

The bends, or rather gentle curves, in the horn. are located such that the bending of the. air column occurs where the length of. the; wave front transverse the bend is less than wave; length at 1:0,0oo cycles. The design relative tov such bends is. in keeping with best practice so that performance. up to 10,606 cycles; is: limited only by the. driving unit employed.

The taper lawv employed in the particular design shown is exponential, chosen as being. the most economical of the total and critical space available. Obviously, however, the. novel features of the present invention may be applied to.

a. horn employing any taper law or combination of taper; laws such, for example, as the hyperbolic. law taught by the Salmon Patent No. 2,338,262,. or the multiple taper scheme described by Olson, A Horn Consisting of Manifold Exponential Sections, Journal of Society Motion Picture Engineers, vol. 30, pp. 551, (1938).

Expansion first in a single plane and then in both planes results in a considerably greater latitude in design, permitting the choice of horizontal and vertical radiation angles independent ly of each other. Angles other than those described and illustrated herein are readily attainable by this novel arrangement of expansion. The resultant astigmatism, or fact that the wave front radius of curvature in the vertical plane differs from that in the horizontal plane, does not appear to be a defect from either a theoretical nor practical standpoint.

Broadly the invention comprehends a loud speaker horn of which the component parts are so constructed and arranged that desired angular radiation is provided in the smallest possible length and space commensurate with the requirements of mouth size, throat size and taper rate.

What is claimed is:

1. In a loudspeaker horn, an enclosure forming an air column shape characterized by means forming successive bifurcations whereby the air column is first diverted in a region of small area and with smooth gradual curves into two air columns symmetrically spaced from the original axis by a given angle, and outwardly therefrom each of said air columns is again bifurcated in the same plane as the first bifurcation to give a further angular spread to the emitted wave, and means outwardly from said first means and extending transversely thereof forming additional bifurcations whereby the radiation angle of the horn is determined by the surface boundaries or walls of the horn nearest the mouth thereof.

2. A horn for middle and upper audio frequencies comprising means forming a first length of air column which expands substantially in a first single plane, said means including deflectors to diffuse the sound to the desired angular spread in said plane, said deflectors terminating at an arc where the wave front has been caused to acquire the desired angular spread, means forming a further length of air column having its longitudinal axis in alignment with the longitudinal axis of said first length of air column and in which expansion continues at the same angle in the first plane as established in said first length of air column and also expands in a plane perpendicular to said first plane, and means comprising at least one additional deflector in said further length of air column for diffusing the sound in said second plane.

3. A horn for middle and upper audio frequencies comprising means forming a first length of air column which expands substantially in a first single plane, said means including deflectors to diffuse the sound to the desired angular spread in said plane, said deflectors terminating at an are where the wave front has been caused to acquire the desired angular spread, means forming a further length of air column in which expansion continues at the same angle in the first plane as established in said first length of air column and also expands in a plane perpendicular to said first plane, and means comprising at least one additional deflector in said further length of air column for diifusing the sound in said second plane.

4. In a loudspeaker horn, solid means forming two opposite boundaries which are flat and substantially parallel in a first region near the throat whereby substantially no expansion occurs to flare of said boundaries in such first region and which are curved outwards from each other and flaring in a second region farther from the throat, solid means forming two other opposite boundaries forming with said first boundaries a conduit, said second means comprising an assembly of curved and fiat members forming flare in the region near the throat at a predetermined rate and at a fixed included angle, and contoured pieces fixed to said fiat parts to form a smooth curve'and expansion with the initial curve.

5. A loudspeaker horn in accordance with claim 4 in which the contoured pieces fixed to said flat surfaces are terminated within said horn and short of the horn mouth so that the individual cell mouths formed by said contoured pieces and the outer walls of the horn are small in size, preferably small compared to the shortest wavelength to be transmitted by said horn.

6. A loudspeaker horn in accordance with claim 4 in which the axis of the conduit formed by said boundaries constitutes a single straight line.

PAUL W. KLIPSCH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,067,905 English July 22, 1913 1,477,556 Grissinger Dec. 18, 1923 1,525,320 Pierce Feb. 3, 1925 1,614,983 Fuller Jan. 18, 1927 1,666,057 Grissinger Apr. 10, 1928 1,666,058 Grissinger Apr. 10, 1928 1,666,059 Grissinger Apr. 10, 1928 1,992,268 Wente Feb. 26, 1935 2,001,089 Blattner May 14, 1935 FOREIGN PATENTS Number Country Date 281,792 Great Britain Dec. 15, 1927 

